The applicants propose to study the relationship between age, nutrition and host defense. Preliminary data presented suggest that some of the manifestations of reduced host defense seen in the elderly may be ascribed to protein calorie malnutrition (PCM). Identical immunologic and hematologic abnormalities occur in malnutrition as those which are said to occur as a function of age. In order to accurately assess these relationships, reliable nutritional assessment parameters for the aged must be determined. Preliminary data are presented which indicate a need for such control values and a rational approach to obtain these values has been developed. Phase I of this study will evaluate 200 healthy ambulatory subjects over 60 years of age. Complete nutritional, hematological and immunological assessments will be performed from which control values will be developed. Univariate and multivariate analysis of age, host defense and nutritional parameters should provide information on the modulating effect of nutrition on host defense in the elderly as well as clues to the possible mechanisms. Phase II will determine if aggressive nutritional support given to a cohort of 20 malnourished elderly hospitalized subjects will result in measurable improvement in nutritional parameters and host defense functions. The results should lead to a better understanding of the relationship between nutrition, age and host defense.